Endoscopes and other optical medical instruments have to be sterilized before each use. This sterilization is nowadays carried out by autoclaving, in which the optical instruments undergo a treatment with hot steam at a pressure in excess of 3 bar and a temperature in excess of 130° C.
To ensure that no moisture gets into the instrument housing under high thermal loading, it is known in practice for the terminal end windows, used as cover glasses and/or end lenses, to be connected to the instrument housing in a fluid-tight manner by adhesive bonding, welding or soldering.
An optical instrument of the type in question is known from DE 195 07 205 C2, for example.
However, since the materials used have different coefficients of thermal expansion, considerable stresses always arise, which can lead to cracks and/or stress fractures and, consequently, to loss of sealing.
Moreover, an autoclavable endoscope is known from DE 699 23 388 T2. In order to protect the instrument housing against entry of moisture during autoclaving, a water-tight cap or a nonreturn valve cap is provided that can be secured on the housing of the lens system.
Although these additional cover caps ensure reliable sealing of the instrument housing, this known construction has the disadvantages that, on the one hand, a separate component part has to be made available and, on the other hand, the sealing of the instrument housing necessitates an additional assembly step, namely the attachment of the cover cap.